The present disclosure relates to amide friction modifiers, and more particularly to amide friction modifiers having improved low temperature compatibility with fuels. The present disclosure further relates to fuel compositions including friction modifiers having improved low temperature compatibility, and methods for reducing the friction of a fuel when the fuel is being pumped.
Regulatory mandates requiring the introduction of low sulfur fuels, which are known to be less lubricating, have raised concerns regarding the durability of fuel pumps and injectors. While sulfur itself is not known to be a lubricity modifying agent, the removal of sulfur by deep hydrotreating is known to inadvertently remove natural lubricity components of the fuel, such as certain aromatics, carboxylic acids, and esters. Unfortunately, commercial gasoline detergents and dispersants generally show very little friction reducing characteristics until very high concentrations are added to the fuel. These high detergent concentrations often reach levels where no-harm effects such as combustion chamber deposits (CCD) become unacceptable.
As discussed at some length in U.S. Pat. No. 6,277,158 to McLean, the performance of gasolines and other fuels can be improved through the use of additive technology. It has been suggested that separate friction modifiers can be added to gasoline to increase fuel economy by reducing engine friction. Fuel friction modifiers would also serve to protect high-pressure fuel pumps and injectors, such as those found in direct injection gasoline (DIG) engines, from wear caused by fuel.
In selecting suitable fuel additives it is important to that the additives do not adversely affect engine performance. For example, the additives should not promote valve sticking or cause other performance-reducing problems. To be suitable for commercial use, a friction modifier additive must pass all no-harm testing required for gasoline performance additives. This is often the biggest hurdle for commercial acceptance. The no-harm testing involves 1) compatibility with gasoline and other additives likely to be in gasoline at a range of temperatures, 2) no increase in intake valve deposits (IVD) and CCD, 3) no valve stick at low temperatures, and 4) no corrosion in the fuel system, cylinders, and crankcase. Developing an additive meeting all these criteria is challenging.
Most prior friction modifiers for fuels have been derivatives of natural (plant and animal derived) fatty acids, with only a few purely synthetic products. For example, WO 01/72930 A2 describes a mechanistic proposal for delivery of a fuel born friction modifier to the upper cylinder wall and into the oil sump resulting in upper cylinder/rings and valves lubrication. The friction modifier is packaged with fuel detergent dispersants such as polyetheramines (PEAs), polyisobutene amines (PIBAs), Mannich bases, and succinimides. The WO '930 reference refers to U.S. Pat. Nos. 2,252,889, 4,185,594, 4,208,190, 4,204,481, and 4,428,182, which all describe the use of fuel modifiers in diesel fuel. Chemistries covered by these patents include fatty acid esters, unsaturated dimerized fatty acids, primary aliphatic amines, fatty acid amides of diethanolamine and long-chain aliphatic monocarboxylic acids. Also mentioned therein is U.S. Pat. No. 4,427,562, which discloses a lubricant oil and fuel friction modifier made by reacting primary alkoxyalkylamines with carboxylic acids or by aminolysis of the appropriate formate ester. U.S. Pat. No. 4,729,769 is also referenced and discloses a gasoline carburetor detergent for gasoline compositions derived from reaction products of a C6-C20 fatty acid ester, such as coconut oil, and a mono- or di-hydroxy hydrocarbyl amine, such as diethanolamine. The additive in the '769 patent is described as being useful in any gasoline including leaded and those containing methylcyclopentadienyl manganese tricarbonyl (MMT). The fuel described in the '769 patent may contain other necessary additives such as anti-icers, and corrosion inhibitors.
Various other references disclose friction modifying additives for fuels. For example, U.S. Pat. No. 5,858,029 discloses the reaction of primary etheramines with hydrocarboxylic acids to give hydroxyamides that exhibit friction reduction in fuels and lubricants. Other patents describing friction modifiers include U.S. Pat. Nos. 4,617,026 (monocarboxylic acid of ester of a trihydric alcohol, glycerol monooleate as fuels and lubricant friction modifier); U.S. Pat. Nos. 4,789,493, 4,808,196, and 4,867,752 (use of fatty acid formamides); U.S. Pat. No. 4,280,916 (use of fatty acid amides); U.S. Pat. No. 4,406,803 (use of alkane 1,2-diols in lubricants to improve fuel economy); and U.S. Pat. No. 4,512,903 (use of amides from mono- or polyhydroxy substituted aliphatic monocarboxylic acids and amines). U.S. Pat. No. 6,328,771 discloses fuel compositions containing lubricity enhancing salt compositions made by the reaction of certain carboxylic acids with a component that is comprised of a heterocyclic aromatic amine. EP 0 798 364 discloses diesel fuel additives comprising a salt of a carboxylic acid and an aliphatic amine, or an amide obtained by dehydration-condensation between a carboxylic acid and an aliphatic amine. EP 0 869 163 A1 describes a method for reducing engine friction by use of ethoxylated amines. In addition, U.S. Pat. No. 4,086,172 (oil soluble hydroxyamines such as “ETHOMEEN 18-12™ (formula C18H37N—(CH2CH2OH)2) as lubricant antioxidant); U.S. Pat. No. 4,129,508 (reaction products of succinic acid or anhydride and a polyalkylene glycol or monoether, an organic basic metal, and an alkoxylated amine as a demulsifier); U.S. Pat. Nos. 4,231,883; 4,409,000; and 4,836,829, all teach various uses of hydroxyamines in fuels and lubricants.
U.S. Pat. No. 6,277,158 describes the current practice in the supply of gasoline as generally being to pre-mix the fuel additives into a concentrate in a hydrocarbon solvent base, and then to inject the concentrate into gasoline pipelines used to fill tankers prior to delivery to the customer. To facilitate injection of the concentrate into the gasoline, it is important that the concentrate is in the form of a low viscosity, homogeneous liquid.